Composite structures (or components) are generally made from two or more constituent materials with significantly different physical or chemical properties. When combined, they produce a structure with characteristics different from the individual materials, with the aim of using the benefit of both.
When manufacturing composite structures using a manufacturing process such as Automated Fiber Placement (AFP) or Automated Tape Layering (ATL), inspecting the dimensional requirements of the manufactured structures is an important part of the manufacturing process.
Known methods for performing dimensional inspection involve gathering data via manual inspection using a hand-held probe within a laser tracker system, and comparing the measured data with theoretical data from a Computer-Aided Design (CAD) file. In the case of a composite structure having many plies, manual inspection of the fibers of each ply of the structure is extremely time consuming. Another shortcoming of manual inspection is that it is dependent on the hand and eye skills of the operator, which makes it harder to validate and certify the inspection at a later time, due to the repeatability criteria required for the certification and validation procedure.
Online inspection systems are capable of acquiring images and performing some sort of measurement and/or analysis while a ply is being laid-up. The inspection occurs during manufacturing and does not need to be performed after the lay-up of a ply has been performed. For this to be feasible, the position in space of a point on a ply needs to be accurately known. Online inspection systems having a camera attached to the head of a manufacturing robot tend to rely on robot positioning accuracy, which is known to be poor for performing measurements and for accurately determining a position in space.
Therefore, there is a need to address the issue of referencing the ply in space for automated manufacturing processes.